Cytology is the branch of biology dealing with the study of the formation, structure, and function of cells. As applied in a laboratory setting, cytologists, cytotechnologists, and other medical professionals make medical diagnoses of a patient's condition based on visual examination of a specimen of the patient's cells. A typical cytological technique is a “Pap smear” test, in which cells are scraped from a woman's cervix and analyzed in order to detect the presence of abnormal cells, a precursor to the onset of cervical cancer. Cytological techniques are also used to detect abnormal cells and disease in other parts of the human body.
The conventional human review process for Pap smear analysis involves the manual screening of microscopic samples on a slide by a cytotechnologist. The cytotechnologist systematically views the tens of thousands of cells on a slide, typically at low magnification, to identify areas of interest, which are manually marked. The pathologist then views each identified area at high magnification, in order to distinguish abnormal cells by comparing the size, shape, and density of the cells located in the area against established criteria. The diagnostic Pap smear has suffered from a high false negative rate due to the tedium and fatigue associated with this exhaustive search. Because of the high false negative rate, many abnormalities remain undetected or are detected too late.
About one third of the false negative results have been associated with screening errors. In order to reduce screening errors, computer imaging has been applied to the automation of Pap smear analysis. Pre-screening systems have been developed which sort out the potentially abnormal specimens from among the high number of normal specimens, so that the number of normal specimens requiring full human reading can be reduced. These automated pre-screening systems can, however, also cause false readings because of inaccurate readings by the systems.